Apparatus and method for tracking feature&#39;s position in human body

ABSTRACT

A method for tracking position of a feature in a subject is provided comprising operating a CT scanner to generate and display CT images of a volume within the subject and operating the CT scanner to generate projection X-Ray images of the volume. The X-Ray images are responsive to X-Ray emitted by two X-Ray sources displaced from each other. The method further comprises generating and displaying stereoscopic images from said projection X-Ray images, wherein the stereoscopic images are spatially registered to the CT images.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending, commonly assigned U.S.patent application Ser. No. 12/419,801, filed Apr. 7, 2009, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/123,584,filed Apr. 10, 2008, the entire contents of each of which areincorporated herein by reference, as if fully set forth herein.

FIELD OF THE INVENTION

The invention relates to tracking position of organs, lesions or devicesin the human body, and more specifically it to application of ComputedTomography (CT) and Stereoscopic Fluoroscopy imaging techniques duringinterventional procedures.

BACKGROUND OF THE INVENTION

Medical procedures that require tracking of the position of a lesion ordevice in the human body are very common. A lesion is referred to hereinas a tumor, diseased artery or any other diseased or target tissue. Forexample, in percutaneous coronary intervention (PCI) procedures aballoon is inserted through a catheter from an artery in the groin to anarrowed section in a coronary artery. The balloon is then inflated,compressing the plaque and dilating the narrowed coronary artery so thatblood can flow more easily. This is often accompanied by inserting anexpandable metal stent.

The procedure is monitored by X-Ray imaging technique referred to asangiography, which combines fluoroscopic projection imaging of multipleimages per second and infusion of contrast agent (also referred to asdye) to the arteries to be viewed. Using angiography, the physician canview and identify the narrowing in the artery, direct the balloon andstent to position and verify correct positioning of the stent.

However, conventional fluoroscopy or angiography provide 2D projectionimages and do not disclose the complete 3D structure underneath. The 3Dstructure of human organs can be viewed by techniques such as ComputedTomography (CT) or MRI.

CT scanners are used routinely in medical, homeland security and otherfields. In a typical CT scanner there is an X-Ray source and arraydetector, both mounted on a gantry and made to rotate about a scannedsubject. Radiation that was attenuated by the scanned subject isreceived by the detector, acquired and reconstructed to produce imagesof tomographic cross sections, also called “slices”. The slice imagesare stored on computer media, displayed and optionally processed to 3Dimages.

CT scanners can acquire, reconstruct and display single or severalslices in almost real time. However, CT scanners typically requireminutes to scan a whole organ, reconstruct the slice images and processthe data to 3D presentation. Therefore, CT scanners cannot typically beused for real time monitoring of position in three dimensions duringinterventional procedures.

One solution known in the art is to carry out a CT scan of the subjectand generate volumetric images. Subsequently, in a different sessionusing a different system, real time 2D fluoroscopy or other real timeimaging is performed wherein the CT images are used as a guidingroadmap. Some exemplary clinical applications where combination of 2Dfluoroscopy and 3D CT images may be beneficial are neural interventionsand electrophysiology interventions such as RF ablation and leadplacement procedures. The disadvantage is that the two sets of imagesare not acquired under identical conditions of the scanned subject andare not registered respective of each other in space, thereby limitingthe accuracy.

CT scanners using a cone beam X-Ray source and a large area arraydetector are also known in the art. It has been noted that the largearea CT detector can be used in association with the cone beam source togenerate fluoroscopic or angiographic 2D images. Substantially themethod involves positioning the gantry carrying the source and detectorat a given rotation angle wherein the subject is in the radiation field,acquiring attenuation data, processing the data and displaying multiple2D images per second.

U.S. Pat. No. 6,198,790 to Pflaum et al., the content of which isincorporated herein by reference, discloses an X-ray diagnosticapparatus having a computed tomography device including a first X-raytube, which is fastened to a gantry ring and which emits a fan-shapedeffective beam, and an opposed radiation receiver, which is formed by arow of individual detector elements, each of which forms an electricalsignal corresponding to the received radiation intensity. A second X-raytube is additionally fastened to the gantry ring at a right angle to thefirst X-ray tube, opposite which, at the gantry ring, a matrix-likeX-ray detector is arranged. The second X-ray tube is activated inspecified rotational positions in pulsed fashion, such as at theuppermost rotational point. X-ray shadowgraphs thus can be producedsimultaneously with CT images and without a need for repositioning anyof the apparatus components.

U.S. Pat. No. 7,164, 745 to Tsuyuki, the content of which isincorporated herein by reference; discloses X-ray computed tomographyapparatus for medical diagnosis, reconstructs tomographic image based ondetection of X-rays penetrated through patient, and creates fluoroscopicimage on plane that is perpendicular to X-ray path.

CT scanners using multiple cone beam sources are also known in the art.Multiple X-Ray sources may be distributed azimuthally about the rotationaxis, or along an axis parallel to the rotation axis (Z axis), or both.Of interest to us are configurations wherein the sources are relativelyclose to each other and are irradiating a common detector array suchthat the multiple beams are at least partially overlapping.

Some disclosures that cover such geometries are application U.S. PatentPublication No. 2006/285633 A1 to Sukovic et al.; PCT Publication Nos.WO 2006/038145 A to Koken et al. and WO 2008/122971 A1 to Dafni, andwhich is assigned to the assignee of the present invention, the contentof which is incorporated herein by reference.

It has been noted that overlapping beam from multiple X-Ray sourcesoperating asynchronously can be used for stereoscopic visualization.Some disclosures are U.S. Pat. No. 5,233,639 to Marks; U.S. Pat. No.4,819,255 to Sato; U.S. Pat. No. 4,712,226 to Horsbaschek; and U.S. Pat.No. 6,181,768 to Berliner, the contents therein are incorporated hereinby reference. Several publications discuss X-Ray stereoscopic imaging inconnection to angiography: “Machine precision assessment for 3D/2Ddigital subtracted angiography images registration”, Proceedings of SPIEMedical Imaging 1998, K. Hanson Ed, vol 3338, pp. 39-49, 23-26 February1998, and “Application of Stereo Techniques to Angiography: Qualitativeand Quantitative Approaches” Jean Hsuy et. al., Purdue University, allincorporated herein by reference.

However, devices incorporating the 3D imaging capabilities of CTscanners and stereoscopic fluoroscopy or angiography in the same systemare not known in the art. It is the purpose of this invention to providesuch a device and thereby gain the benefits of accurate spatialregistration between the two sets of images, as well as the benefits ofan efficient clinical workflow.

SUMMARY OF THE INVENTION

The invention relates to tracking position of organs, lesions or devicesin the human body, and more specifically it to application of ComputedTomography (CT) and Stereoscopic Fluoroscopy imaging techniques duringinterventional procedures.

According to an aspect of the current invention, a CT scanner forscanning a subject is provided, the scanner comprising: a gantry rotorcapable of rotating about a scanned subject; at least two cone beamX-Ray sources displaced from each other mounted on said gantry; at leastone 2D detector array mounted on said gantry, said detector is capableof receiving radiation emitted by said at least two X-Ray sources andattenuated by the subject to be scanned; a first image processor capableof generating and displaying CT images of a volume within the subject; asecond image processor capable of generating projection X-Ray images ofsaid volume, wherein the images are responsive to X-Ray separatelyemitted by each of said at least two cone beam X-Ray sources; and athird image processor capable of generating and displaying fluoroscopicimages composed of said projection X-Ray images, wherein saidfluoroscopic images are spatially registered to said CT images.

In some embodiments, any of said first image processor, second imageprocessor and third image processor are incorporated into a single imageprocessor.

In some embodiments, the at least two X-Ray sources are displaced fromeach other along a direction parallel to the rotation axis of saidgantry.

In some embodiments, said at least two X-Ray sources are displaced fromeach other azimuthally respective of the rotation axis of said gantry.

In some embodiments, said at least two X-Ray sources comprise two X-Raysources.

In some embodiments, said two sources of the at least two X-Ray sourcesare operative for generating stereoscopic images.

In some embodiments, said fluoroscopic images are generated followinginjection of contrast agent.

In some embodiments, said fluoroscopic images are generated anddisplayed multiple times per second.

In some embodiments, said fluoroscopic images are generated anddisplayed one at a time.

In some embodiments, said fluoroscopic images are displayed overlayingan image derived from said CT images.

In some embodiments, said fluoroscopic images are displayed side by sidewith said CT images.

In some embodiments, a graphic mark indicating position of a featurewithin said volume is overlaid said CT images wherein said position ofthe feature within said volume is computed responsive to the position ofthe feature in said projection X-Ray images.

In some embodiments, said fluoroscopic images are used to position aninterventional device respective of a lesion.

In some embodiments, said fluoroscopic images are displayed instereoscopic form.

In some embodiments, said an algorithm is used to calculate the depth ofa feature in said fluoroscopic images.

In some embodiments, the images are acquired responsive to heart monitorsignal.

In some embodiments, said images are acquired responsive to breathingmonitor signal.

In some embodiments, said multiple X-Ray sources comprise a single X-Raytube housed within a single vacuum enclosure wherein said tube hasmultiple focal spots.

In some embodiments, said multiple X-Ray sources comprise multiple X-Raytubes.

According to another aspect of the current invention, a method fortracking position of a feature in a subject is provided, the methodcomprising the steps of: operating a CT scanner to generate and displayCT images of a volume within the subject; operating said CT scanner togenerate projection X-Ray images of said volume wherein said images areresponsive to X-Ray emitted by two X-Ray sources displaced from eachother; and generating and displaying stereoscopic images from saidprojection X-Ray images, wherein said stereoscopic images are spatiallyregistered to said CT images.

In some embodiments, the CT scanner comprises two X-Ray sources.

In some embodiments, the CT scanner comprises more than two sourceswherein at least two sources are operative for generating stereoscopicimages.

In some embodiments, the method further comprising injecting contrastagent to the subject.

In some embodiments, said stereoscopic images are generated anddisplayed multiple times per second.

In some embodiments, said stereoscopic images are generated anddisplayed one at a time.

In some embodiments, said stereoscopic images are displayed overlayingsaid CT images.

In some embodiments, said stereoscopic images are displayed side by sidewith said CT images.

In some embodiments, a graphic mark indicating position of a featurewithin said volume is overlaid said CT images wherein said position ofthe feature within said volume is computed responsive to the position ofthe feature in said projection X-Ray images.

In some embodiments, the method further comprising positioning aninterventional device respective of a lesion or specific anatomicstructure using said stereoscopic images.

In some embodiments, the method further comprises identifying the lesionor specific anatomic structure using CT images.

In some embodiments, the method further comprising verifying theposition of said interventional device respective said lesion orspecific anatomic structure using CT images, wherein the positioningprocess is guided by said stereoscopic images.

In some embodiments, the method further comprising acquiring imagesresponsive to heart monitor signal.

In some embodiments, the method further comprising acquiring imagesresponsive to breathing monitor signal.

According to yet another aspect of the current invention, a CT scannerfor scanning a subject is provided, the scanner comprising:

-   -   a gantry stator;    -   a CT subsystem comprising:    -   at least one gantry rotor, mounted on said gantry stator capable        of rotating about a scanned subject; a CT X-Ray source mounted        on said at least one rotor; a CT X-Ray detector array mounted on        said at least one rotor; wherein said CT X-Ray source and said        X-Ray detector are configured to rotate together about said        scanned subject, and wherein said CT detector array is capable        of receiving radiation emitted by said CT X-Ray source and        attenuated by the subject to be scanned; and a first image        processor capable of generating and displaying CT images of a        volume within the subject; and    -   a fluoroscopy subsystem comprising:    -   at least a first and a second cone beam X-Ray sources displaced        from each other mounted on said at least one rotor; a 2D        detector mounted on said on said at least one rotor, wherein        said at least a first and a second cone beam X-Ray sources and        said 2D detector array are configured to rotate together about        said scanned subject, and wherein said 2D detector is capable of        receiving radiation emitted by said at least first and second        X-Ray sources and attenuated by the subject to be scanned; and a        second image processor capable of generating projection X-Ray        images of said volume, wherein the images are responsive to        X-Ray separately emitted by each of said at least first and        second cone beam X-Ray sources; and    -   a third image processor capable of generating and displaying        fluoroscopic images composed of said projection X-Ray images,        wherein said fluoroscopic images are spatially registered to        said CT images.

In some embodiments, the said CT subsystem and said fluoroscopysubsystem are mounted on the same gantry rotor.

In some embodiments, the said CT subsystem and said fluoroscopysubsystem are mounted substantially perpendicular to each other.

In some embodiments, the said at least one gantry rotor comprises afirst and a second gantry rotors configured to independently rotateabout said subject, and wherein said CT subsystem is mounted to saidfirst gantry rotor, and said fluoroscopy subsystem is mounted on saidsecond gantry rotor, and wherein said first and second gantry rotors aremounted on said gantry stator.

In some embodiments, said fluoroscopic images are displayed instereoscopic form.

In some embodiments, a graphic mark indicating position of a featurewithin said volume is overlaid said CT images wherein said position ofthe feature within said volume is computed responsive to the position ofthe feature in said projection X-Ray images.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. In case of conflict, the patentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary forunderstanding of the invention, the description taken with the drawingsmaking apparent to those skilled in the art how the several forms of theinvention may be embodied in practice.

In the Drawings:

FIG. 1 is an illustration of a prior art cone beam CT scanner.

FIG. 2 is an illustration of a cone beam CT scanner having multipleX-Ray sources, wherein the sources are displaced from each other alongthe Z direction according to an exemplary embodiment of the currentinvention.

FIG. 3 is a side view of a cone beam CT scanner having multiple X-Raysources, wherein the sources are displaced from each other along the Zdirection according to an exemplary embodiment of the current invention,showing the scanned subject shown by a way of example a human patientundergoing imaging of the heart.

FIG. 4 is an illustration of a multiple X-Ray source cone beam CTscanner according to an exemplary embodiment of the current invention,wherein the sources are displaced from each other along the X direction.

FIG. 5 is an illustration of a multiple detector, multiple X-Ray source,CT scanner according to yet another exemplary embodiment of the currentinvention, wherein X-Ray sources 11 f and 11 g are displaced from eachother along the X direction and X-Ray source 11 e is angularly displacedby 90° relative to sources 11 f and 11 c.

FIG. 6 is a description of a method of using a multiple X-Ray source CTin an interventional procedure according to an exemplary embodiment ofthe current invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to tracking position of organs, lesions or devicesin the human body, and more specifically it relates to application ofComputed Tomography (CT) and Stereoscopic Fluoroscopy imaging techniquesduring interventional procedures.

Before explaining the embodiments of the invention in detail, it is tobe understood that the invention is not limited in its application tothe details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

In discussion of the various figures described herein below, likenumbers refer to like parts. The drawings are generally not to scale.

For clarity, non-essential elements were omitted from some of thedrawings.

FIG. 1 is a schematic illustration of a prior art cone beam CT scanner102. X-Ray source, such as X-Ray tube 10 emits a beam of X-radiation 12in the direction of detector array 14. Typically the source-detectorpair is mounted on a rotating gantry and a subject to be examined 18 ispositioned between the source and the detector. A collimator is used toshape the beam to a pyramid shape so as to cover the detector area.Detector array 14 may be composed of array of discrete elements arrangedin rows and columns, a flat panel detector or the like. Detector array14 may optionally have a spherical shape or planar shape, or have othersurface curvature. Detector array 14 may, as shown for illustrations inthese figures have an arc shape (a section of a cylinder) centered aboutthe focal spot. Herein below we refer to “rows” of the detector array,as the row of detector elements in the X direction of the detector,perpendicular to the rotation axis (Z direction).

The coordinate system shown in FIG. 1 refer to the rotating gantry suchthat the Z axis is parallel to the rotation axis, and the Y axis pointsfrom the center of detector array to the X-Ray source at any rotationangle.

Various parts of CT scanner 102, including the gantry, X-Ray sourcecollimator for shaping the X-Ray beam, patient support, data acquisitionsystem, controller, image processor, display unit and other parts arenot shown in FIG. 1 and subsequent figures for clarity. However, aperson skilled in the art will appreciate that these parts are includedin the described embodiments and are operative as a part of theembodiments.

CT scanner 102 acquires data while the gantry rotates around the subject18, acquiring multiple two dimensional data sets at different rotationangles. A three dimensional tomographic image is than reconstructedusing cone beam reconstruction algorithms as known in the art.

FIG. 2 is an illustration of a cone beam CT scanner 104 having multipleX-Ray sources, wherein the sources are displaced from each other alongthe Z direction according to an exemplary embodiment of the currentinvention.

X-Ray sources 11 a and 11 b emit X-Ray beams 13 a and 13 b,respectively. Beams 13 a and 13 b are attenuated by subject 18 andimpinge on detector array 14. Beams 13 a and 13 b are overlapping withinat least a certain volume of subject 18.

In one mode of operation, CT scanner 104 may optionally be used togenerate rotational CT images using both X ray sources as described,e.g., in applications U.S. Patent Publication No. 2006/285633 A1 toSukovic et al., and PCT Publication Nos. WO 2006/038145 A to Koken etal., or WO 2008/122971 A1 to Dafni. Alternatively, CT scanner 104 mayoptionally be used to generate rotational CT images using one X-Raysource. CT images may be acquired in any scan mode known in the art, bya single shot, in “step and shoot” mode or by spiral (helical scanning).

In a second mode of operation, the gantry of CT scanner 104 may bestationary at a desired rotation angle and subject 18 may be imaged by2D projection imaging using X-Ray sources 11 a and 11 b and detector 14.In this mode the data acquisition system, image processor and displaysystem are operative similar to a digital radiography or a digitalfluoroscopy system.

It should be noticed, that the two-dimensional (2D) image detected byarray 14 in response to X-Ray beam propagating through subject 18 is aprojection of the three-dimensional (3D) distribution of the tissuedensity of subject 18, as seen from the view-point of the X-Ray source.Thus, images created when source 11 a is operational, are slightlydifferent than the images detected when source 11 b is operational. Bysequentially operating both X-Ray sources, one at a time, stereoscopicviews of the 3D subject 18 may be obtained. By electronicallycontrolling the sources 11 a and 11 b, the time difference betweenacquiring two images, one using X-Ray beam 13 a and the other usingX-Ray beam 13 b may be short, minimizing or eliminating movement of thesubject 18 between the two images acquisition. By a way of non limitingexamples, each of sources 11 a and 11 b may be operated, for example, 15or 25 or 30 or 60 times a second, for a pulse duration of, for example,1 or 5 or 10 or 15 milliseconds each. However, other pulse frequenciesand durations may be used.

In some embodiments, X-Ray sources 11 a and 11 b are two separate X-Raytubes.

In other embodiments, sources 11 a and 11 b are two X-Ray sources withinone vacuum enclosure.

In some exemplary embodiments, the sources are associated with separatepairs of anodes and cathodes for each source.

In some exemplary embodiments, the sources are associated with a singleanode and cathode arrangement wherein switching between source positionsis accomplished by magnetic or electric deflection of electron beam fromthe cathode. Fast switching of the radiation on and off and between thesources may optionally be achieved by methods known in the art such aspulsing the high voltage supply energizing the X-Ray sources or byapplication of grids. A person skilled in the art will appreciate thereare other methods to provide multiplicity of X-Ray sources spaced apartand to pulse the radiation and such other methods are covered by thecurrent invention.

It should be noted that since generally the two X-Ray sources areworking one at a time, one high voltage generator may optionally be usedfor both sources.

In contrast to acquisition of stereoscopic views, where the gantry isstationary, and sources 11 a and 11 b are alternation their operation;as described above a CT image may be obtained by rotating the gantry andusing one of sources 11 a and 11 b. Alternatively a third, CT dedicatedX-Ray source (not seen in these figures) may be used for acquiring CTdata.

System 104 is useful for embodiments of the present invention asdescribed hereinbelow.

FIG. 3 is a side view of a cone beam CT scanner having multiple X-Raysources 104, wherein the sources are displaced from each other along theZ direction according to an exemplary embodiment of the currentinvention, showing the scanned subject 18 shown by a way of example ahuman patient undergoing imaging of the heart.

For clarity, X-ray sources 11 a and 11 b are represented in this figureby their X-Ray focal points 11 a′ and 11 b′

Striped region 20 marks the volume of the examined region wherein thebeams 13 a and 13 b overlap. Stereoscopic images of the overlappingregion 20 may be obtained while the gantry is stationary.

FIG. 4 is an illustration of a multiple X-Ray source, cone beam CTscanner 106 according to another exemplary embodiment of the currentinvention, wherein X-Ray sources 11 c and 11 d are displaced from eachother along the X direction.

In contrast to the embodiment depicted in FIGS. 2 and 3, X-Ray sources11 c and 11 d are displaced from each other along the X direction. X-Raysources 11 c and 11 d emit beams of X-radiation 13 c and 13 d,respectively, beam 13 c and 13 d, are attenuated by subject 18 andimpinge on detector array 14. Beams 13 c and 13 d are overlapping withinat least a certain volume of subject 18. System 106 is useful forembodiments of the present invention as described hereinbelow.

It should be noted, that stereoscopic viewing requires acquisition twoimages from viewpoints separated by a substantial angular separation.Thus, more than two sources may be used, and a pair of images selectedfor stereoscopic viewing. It should be noted that the separation of thetwo X-Ray sources may optionally be at a direction other than purelyalong the X or the Y axis, for example along the vector {A*X, B*Y} whereA and B are arbitrary scalars.

FIG. 5 is an illustration of a multiple detector, multiple X-Ray source,CT scanner 108 according to yet another exemplary embodiment of thecurrent invention, wherein X-Ray sources 11 f and 11 g are displacedfrom each other along the X direction and X-Ray source 11 e is angularlydisplaced by 90o relative to sources 11 f and 11 c.

In contrast to the embodiment depicted in FIGS. 2 3 and 4, system 108comprises a CT subsystem comprising an X-Ray source 11 e and a CTdetector 14 a. The CT subsystem may be a conventional CT subsystemcomprising a fan beam source and a single slice detector 14 a.Alternatively, detector 14 a may be a multi slice detector havingmultiple rows of detector elements as known in the art. A 3D CT imagemay be acquired by helical or step and shoot scanning by advancing thepatient table or by translating the gantry or by a single shot providingthe detector is wide enough. The CT images are made to overlap stereofluoroscopic images acquired by fluoroscopic subsystem comprisingdetector 14 b and X-Ray sources 11 f and 11 g.

Fluoroscopic detector 14 b is illuminated by at least two X-Ray sources11 f and 11 g producing the at least two cone beams 13 f and 13 grespectively.

In the depicted embodiment, X-Ray sources 11 f and 11 g are displacedfrom each other along the X direction. However, it should be noted thatX-Ray sources 11 f and 11 g may be oriented along the Z axis or along anarbitrary axis.

X-Ray sources 11 f and 11 g emit cone beams of X-radiation 13 f and 13g, respectively, beam 13 f and 13 g, are attenuated by subject 18 andimpinge on detector array 14 b. Beams 13 f and 13 g are overlappingwithin at least a certain volume of subject 18. Fluoroscopic detector 14b may be a flat detector or a curved detector. It should be noted thatthe combination of sources 11 g and 11 f and detector 14 b may beoptimized for fluoroscopic imaging while the combination of source 11 eand detector 14 a may be optimized for CT imaging.

In the depicted embodiment, CT subsystem is oriented substantiallyperpendicular to the fluoroscopic subsystem, however, other orientationsmay be used. For example, the CT subsystem and the fluoroscopicsubsystem may be installed on two independent rotors. For example thetwo rotors may be located on two opposite sides of the same gantrystator. Subject 18 may be at the same position for the CT andfluoroscopic imaging or may be translated between the two modes ofimaging in as long the relative position is registered.

System 108 is useful for embodiments of the present invention asdescribed hereinbelow.

Exemplary embodiments according to the present invention make use of amultiple source CT scanner such as system 104 106 or 108, capable ofproducing volumetric CT images. Further, the systems in exemplaryembodiments are preferably capable of generating stereoscopicfluoroscopy images. By fluoroscopy we refer to multiple X-Ray projectionimaging per second. By angiography we refer to fluoroscopy imaging ofthe cardiovascular system assisted by injection of contrast agent (Dye).Optionally embodiments of the present inventions are used in connectionwith injection of contrast agent. Stereoscopic images are generatedwherein the gantry is positioned at a certain rotation angle and thesources are made to irradiate the subject 18 alternatively. Typicallyeach source generates 15 or 25 or 30 pulses a second although higherlower or other rates are also possible. Optionally, a single shot byeach source is preferably used to generate a single stereoscopicradiographic image. Optionally, data from a plurality of images iscombined to improve image quality. The common detector 14 of system 104or 106 (14 b in system 108) is operative to receive separatelyattenuation images for each source. The reconstruction and display ofthe stereoscopic images are described hereinbelow.

Data provided by detector array 14 (14 b for system 108) is preferablycomputer-processed using conventional techniques known in the field ofX-Ray fluoroscopy to generate real time planar image data for each ofbeams 13 a and 13 b, for example respective of system 104, (andsimilarly beams 13 c and 14 d for system 106; beams 13 f and 13 g forsystem 108). According to the invention, the two images are optionallyemployed to create a composite stereo image for viewing by an operator.The stereo image may be used by the operator to position aninterventional device, such as a catheter, angioplasty balloon, stentand the like, relative to a lesion in the patient body as describedbelow.

For stereo visualization, the computer generated planar stereo componentimages are arranged to be viewed separately by the left and right eyesof an operator so that the two separate images are integrated by theoperator's brain into a three-dimensional image. An offset of betweenabout four degrees and ten degrees, preferably between four and sevendegrees, for example, about six degrees, yields good results. However,other values of angular separation between the two viewpoints used forgenerating the stereoscopic images may be used.

Many ways are known for presenting spaced image data to create astereoscopic effect, and any suitable presentation method may beemployed. For example, the separate images may be viewed using a headmounted electro-optically switched viewer, e.g., of the kind shown in.U.S. Pat. No. 4,214,267 to Roese et al., the content of which isincorporated herein by reference. In such an arrangement, separateviewing windows are provided for each eye. The two images are displayedon a single monitor in alternating fashion, but the viewing windows arealternatively blocked in synchronization with the alternating images soone image is viewable only by the left eye, and the other image isviewable only by the right eye.

Alternatively, separate monitors may be provided in a head-mountedviewer to display only one image for each eye.

Another option is to employ the so-called “autostereo” displaytechnology. As known to those skilled in the art, this is a conventionaltechnology in which a single monitor is designed to display two imagesin such a way that one image is visible only to the left eye, and theother image is visible only to the right eye. Several ways to implementthis are known, and autostereo monitors are available commercially fromseveral sources (e.g., Sharp Corp. 3D LCD; and QinetiQ Group PLC, 85Buckingham Gate, London SW1E 6PD).

Some exemplary embodiments of the present invention acquiresubstantially simultaneous fluoroscopic images from two sources but donot actually display stereoscopic images. In these embodiments thestereoscopic images are optionally displayed side by side. Optionally,computer algorithm is used to estimate the depth of a feature seen in 2Dfluoroscopy images within the 3D volume based on the differences betweenthe two fluoroscopic images and the known system geometry. In theseexemplary embodiments the angular separation between the viewpoints isoptionally increased compared to embodiments used for stereoscopicvisualization. Optionally, each fluoroscopic X-Ray source may beassociated with a separate X-Ray detector.

FIG. 6 is a description of a method of using a multiple X-Ray source CTsuch as system 104, 106 or 108, in an interventional procedure accordingto an exemplary embodiment of the current invention.

According to an exemplary method of the current invention, system 104106 or 108 is first used 202 to acquire CT images of a volume ofinterest. The system than reconstruct and display 204 the volumetricdata. The CT images may be acquired responsive to radiation from asingle X-Ray source or multiple X-Ray sources. It is to be understoodthat CT volumetric data is typically image processed by methods known inthe art for optimal visualization of the tissues of interest, forexample, parts of the cardiovascular system. CT images may be visualizedas a rendered 3D volume, 3D surface rendered, 2D slices in anyorientation, slab of such slices or any other visualization method knownin the art. Alternatively or additionally other known image enhancementmethods may be used such as: contrast enhancements edge enhancement;image smoothing and filtering; and using false colors.

The operator determines 206 the location of the lesion of interestwithin the scanned volume and optionally marks the lesion on at leastone image by graphic overlay.

Subsequently the operator initiates interventional procedure 208involving insertion of at least one device to the patient body. Oneexample for such interventional procedures is cardiac catheterizationwherein the lesions of interest might be stenoses in the coronaryarteries and the devices of interest might be guide wires, catheters,balloons, stents, IVUS probes and the like. Another example for suchinterventional procedure is needle biopsy wherein the lesion of interestis a suspected tumor and the device of interest might be a biopsyneedle. Many other interventional procedures and variations thereof areknown in the art and are covered by this invention. The tracked devicesmight be tools used in the procedure and removed from the body at theend of the procedure, such as catheters and biopsy needles. The trackeddevices might also be devices implantable in the body such aspercutaneous implantable aortal valves, pacemaker leads, stents,brachytherapy seeds, orthopedic devices and the like.

Generally, interventional procedure 208 is performed under prior artfluoroscopy viewing with or without prior CT imaging. According to thecurrent invention fluoroscopy 210 is used following CT imaging withinthe same session.

The CT imaging (202) and subsequent fluoroscopy imaging (210) may beassisted by injection or infusion of contrast agent (dye) or may beperformed without contrast agent.

In order to track the position of the interventional device, theoperator is positioning the gantry having multiple X-Ray sources system104, 106 or 108 in a suitable angle respective of the patient andoperates the system in fluoroscopy mode 210. The operation of the systemin fluoroscopy mode is described in FIGS. 2, 3, 4 and 5. Fluoroscopicimages may be generated and displayed to the operator in real time asthe procedure proceeds. Fluoroscopic images may be dynamically displayed15 or 25 or 30 times a second or at a different rate or a singlefluoroscopic image may be acquired and displayed at a time.Alternatively, a single shot image may be displayed. The operator maychoose to change the gantry angle during the procedure. Fluoroscopicimages may be displayed side by side or optionally displayed instereoscopic form as described herein above.

In addition the fluoroscopy images may be displayed overlaid over the 3DCT image 212 so that the operator can appreciate 214 the position of thedevice relative to the organ and the lesion of interest. Optionally,different colors are used for the CT and fluoroscopy images to enablethe user to differentiate between the two overlaid images. Alternativelythe fluoroscopy images may be displayed side by side with the CT imageswherein overlaid graphic markers indicate same positions on the two setsof images. Graphic mark may be positioned manually by the operator atthe device position on the fluoroscopy image and displayed automaticallyon the CT images. Alternatively or additionally, an algorithm is usedfor detecting the position of the device in the fluoroscopy images andautomatically overlaying it over the CT images as a graphic mark. Inexemplary embodiments, algorithm for detecting position of a device inthe 3D volume is based on the stereoscopic nature of the fluoroscopyimages and the position of the device as appears in the pairs offluoroscopy images corresponding to two different source viewpoint.Optionally such algorithms are used to compute the position of a devicetip, radio-opaque marker or a distinct anatomical feature.

Assuming a well defined and identified feature such as needle tip,catheter tip or a radio-opaque marking appears in both projection imagesit is possible to calculate the position in the 3D volume usingtrigonometry because each point in the projection images represents aline-of-view in the volume and the intersection of the two lines givesthe 3D position of the feature. The calculated location of the featuremay be marked on the registered 3D CT image.

If at least two such features are identified on a thin straightinstrument such as a needle, the location and direction of theinstrument may be calculated and marked on the 3D CT image and on thefluoroscopic images. Similarly, identifying and calculating the locationof at least three points on an instrument is sufficient for calculatinglocation and orientation of an instrument in space. By locating aninstrument, an knowing the shape and construction of the instrument,locations of radio-transparent parts may also be calculated and markedon the 3D CT image and on the fluoroscopic images. These calculationsmay be performed automatically using image processing software known inthe art.

It is to be understood that overlaying CT and fluoroscopic images orcorrelating position in the two sets of images includes optionallytranslation of images to same coordinate system (registration) andoptional remapping of the CT images to correct for sources-detectorgeometry effects. Positional and angular sensors in the gantry and thepatient table enable automatic registration of the fluoroscopic imageswith the CT reconstructed image. The system controller may be operativeto automatically change the viewing direction of the volumetric CTimages according to the fluoroscopy imaging angle so the two sets ofimages will be viewed from same direction respective of the patient.

Accurate positioning of the 2D images respective of the CT images isprovided in the inventive system because both CT and fluoroscopy sets ofimages are acquired at the same session on the same imaging system whilethe patient is laid on the same support frame. Therefore, there is anaccurate geometrical registration between the sets. Optionalstereoscopic visualization according to the present invention providesthe operator with depth perception, not available with conventionalsingle source fluoroscopy, and better association of the fluoroscopicimages with the 3D CT image. Alternatively, the fluoroscopy images aredisplayed side by side. Optionally, a computer algorithm may be used tocorrelate the position of a feature in the at least two fluoroscopicimages and the CT images more accurately than possible with prior artsystems have a single fluoroscopic view direction.

The positioning of the interventional device is iterative, comprising ofrepeated steps of manipulating the device 208, and stereoscopicfluoroscopy visualization 212, 214. Once the positioning is completed216, the operator may optionally choose 218 to perform optionalverification by repeated CT imaging 220 and viewing 222 the deviceposition in the CT image.

Persons skilled in the art will appreciate that the sequence ofoperations described in FIG. 5 is provided by a way of example and forvarious interventional procedures different sequences of operationscombining CT imaging and registered stereoscopic fluoroscopy imaging arepossible, and are included in the scope of this invention.

Certain organs in the patient body move perpetually even if the patientis still. These include for example the heart motion and breathingmotion. According to some exemplary embodiments of the present inventionan optional ECG system is provided to monitor the heart cycle phase. CTimaging and fluoroscopy imaging are optionally gated (prospectively orretrospectively) by the ECG so that imaging is done at a phase ofminimal motion and at the same phase for the two imaging modes, therebyproviding accurate registration. Other types of heart cycle monitorsknown in the art are also useable in embodiments of the invention.

According to some embodiments of the present invention, the patient isinstructed to hold breathing during imaging at a given level of lungsfilling (for example maximum or minimum or other level of filling).According to other preferred embodiment a breathing sensor as known inthe art is provided and used for gating of the imaging. According tosome embodiments, both heart cycle and breathing cycle monitoring gatingare provided.

CT systems 104 and 106 with two sources are given by a way of examplebut systems with a larger number of X-Ray sources may be used as well.Further, multiple source systems with more than two sources may beprovided, wherein different pairs of sources may be used forstereoscopic imaging. For example, a single or a multiple X-Ray sourcemay be used for CT imaging and a different pair of sources may be usedfor stereoscopic imaging.

CT systems 104 and 106 with a single detector are given by a way ofexample but systems more than one detector may be used as well, asdemonstrated by system 108 in FIG. 5. Further, multiple source systemswith more than one detector may be provided, wherein one detectorassociated with multiple X ray sources may be used for stereoscopicimaging and a second detector associated with a single or multiple X raysources may be used for CT imaging.

The multiple X-Ray sources may be provided as separate X-Ray tubes, asingle X-Ray tube housed within one vacuum enclosure wherein said tubehas multiple focal spots or by any other technique known in the art.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub combination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

1. A method for tracking position of a feature in a subject comprisingthe steps of: operating a CT scanner to generate and display CT imagesof a volume within the subject; operating said CT scanner to generateprojection X-Ray images of said volume wherein said X-ray images areresponsive to X-Ray emitted by two X-Ray sources displaced from eachother; and generating and displaying stereoscopic images from saidprojection X-Ray images, wherein said stereoscopic images are spatiallyregistered to said CT images.
 2. A method according to claim 1, whereinthe CT scanner comprises two X-Ray sources.
 3. A method according toclaim 1, wherein the CT scanner comprises more than two sources whereinat least two sources are operative for generating stereoscopic images.4. A method according to claim 1, further comprising injecting contrastagent to the subject.
 5. A method according to claim 1, wherein saidstereoscopic images are generated and displayed in a sequence selectedfrom a group comprising: multiple times per second; and one image at atime.
 6. A method according to claim 1, wherein said stereoscopic imagesare displayed overlaying said CT images.
 7. A method according to claim1, wherein said stereoscopic images are displayed side by side with saidCT images.
 8. A method according to claim 1, wherein a graphic markindicating position of a feature within said volume is overlaid said CTimages wherein said position of the feature within said volume iscomputed responsive to the position of the feature in said projectionX-Ray images.
 9. A method according to claim 1, further comprisingpositioning an interventional device respective of a lesion or specificanatomic structure using said stereoscopic images.
 10. A methodaccording to claim 9, further comprising identifying the lesion orspecific anatomic structure using CT images.
 11. A method according toclaim 9, further comprising verifying the position of saidinterventional device respective said lesion or specific anatomicstructure using CT images, wherein the positioning process is guided bysaid stereoscopic images.
 12. A method according to claim 1, furthercomprising acquiring images responsive to at least one signal selectedfrom a group comprising: heart monitor signal; and breathing monitorsignal.